Fix typo in r364325 that broke tinderbox with -DBUILD_WITH_STRICT_TMPPATH

${TARGET_ARCH} is empty here which results in empy MAKE_PARAMS being
passed to the buildkernel phase. This breaks the build when using the
strict TMPPATH since cc will not be included in $PATH.

Reviewed By:	jhb

Makefile

@@ -734,7 +734,7 @@ universe_kernconf_${TARGET}_${kernel}: .MAKE
 	    ${SUB_MAKE} ${JFLAG} buildkernel \
 	    TARGET=${TARGET} \
 	    TARGET_ARCH=${TARGET_ARCH_${kernel}} \
-	    ${MAKE_PARAMS_${TARGET_ARCH}} \
+	    ${MAKE_PARAMS_${TARGET_ARCH_${kernel}}} \
 	    KERNCONF=${kernel} \
 	    > _.${TARGET}.${kernel} 2>&1 || \
 	    (echo "${TARGET} ${kernel} kernel failed," \